This present invention relates to ultrasound imaging of breast tissue. Women with dense breasts may benefit if an ultrasound exam is done in addition to mammogram. In dense breasts with more glandular tissue than fat, ultrasound may help identify malignant masses not visible by mammography. Fatty tissue produces a black mammogram. Dense breasts, on the other hand, produce a predominantly white mammogram. Detecting a small potentially cancerous calcification which maps as a white dot in the mammogram may be difficult. Ultrasound, on the other hand, may depict cancerous spots as black. Black may be easier to detect in a background of dense highly echogenic, and therefore white, glandular tissue.
Mammograms indicate the average density of the tissue along lines of illumination. Two plates are used to compress the breast tissue to increase the sensitivity to local density variations.
Plates have also been used for imaging a breast with ultrasound. Krueger, et al., xe2x80x9cLimited Angle Ultrasonic Transmission Tomography Of The Compressed Female Breast,xe2x80x9d 1998 IEEE Ultrasonics Symposium, pgs 1345-48 use two plates to fix and compress breast tissue. The top plate through which the transducer insonified the breast was made of polyethylene, and the bottom reflection plate was made of stainless steel. The speed of sound through the breast tissue is measured using time-of-flight data between various transmit/receive element pairs of the transducer. A speed of sound image is superposed on top of a B-Mode image. Frequency dependent attenuation coefficients may also be reconstructed using the same set up and radio frequency data.
Many phase aberration techniques have also been used for general ultrasound imaging. Even though some of phase aberration techniques have demonstrated good performance on phantoms with wire or pin targets, the success may be limited in clinical imaging situations. Many of these phase aberration techniques depend on the assumption that the aberration can be modeled as a phase screen in front of the transducer. This assumption may not apply to breast imaging where the aberration is spatially distributed.
A method and apparatus for ultrasound breast imaging is described. A breast is positioned in between an ultrasound array and a plate with embedded point or line targets. The apparatus and reflections from the targets are used 1) to improve focusing by correcting for tissue delay and amplitude aberration and 2) to improve diagnostics by constructing speed of sound and attenuation coefficient images.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments.